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Today ,more than half of all people in the world

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live in an urban area.

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By mid-century, this will increase to 70%.

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But as recently as 100 years ago,

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only two out of ten people lived in a city,

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and before that, it was even less.

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How have we reached

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such a high degree of urbanization,

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and what does it mean for our future?

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In the earliest days of human history,

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humans were hunter-gatherers,

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often moving from place to place

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in search of food.

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But about 10,000 years ago,

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our ancestors began to learn the secrets

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of selective breeding

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and early agricultural techniques.

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For the first time,

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people could raise food

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rather than search for it,

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and this led to the development

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of semi-permanent villages

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for the first time in history.

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"Why only semi-permanent?" you might ask.

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Well, at first, the villages still had to relocate

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every few years

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as the soil became depleted.

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It was only with the advent of techniques

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like irrigation and soil tilling

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about 5,000 years ago

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that people could rely on a steady

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and long-term supply of food,

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making permanent settlements possible.

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And with the food surpluses

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that these techniques produced,

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it was no longer necessary for everyone to farm.

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This allowed the development

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of other specialized trades,

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and, by extension, cities.

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With cities now producing surplus food,

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as well as tools,

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crafts,

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and other goods,

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there was now the possibility of commerce

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and interaction over longer distances.

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And as trade flourished,

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so did technologies that facilitated it,

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like carts,

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ships,

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roads,

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and ports.

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Of course, these things required even more labor

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to build and maintain,

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so more people were drawn

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from the countryside to the cities

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as more jobs and opportunities

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became available.

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If you think modern cities are overcrowded,

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you may be surprised to learn

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that some cities in 2000 B.C. had population densities

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nearly twice as high as that of Shanghai or Calcutta.

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One reason for this

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was that transportation was not widely available,

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so everything had to be within walking distance,

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including the few sources of clean water

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that existed then.

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And the land area of the city

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was further restricted by the need for walls

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to defend against attacks.

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The Roman Empire was able to develop infrastructure

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to overcome these limitations,

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but other than that,

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modern cities as we know them,

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didn't really get their start

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until the Industrial Revolution,

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when new technology deployed on a mass scale

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allowed cities to expand and integrate further,

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establishing police,

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fire,

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and sanitation departments,

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as well as road networks,

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and later electricity distribution.

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So, what is the future of cities?

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Global population is currently more than 7 billion

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and is predicted to top out around 10 billion.

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Most of this growth will occur

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in the urban areas of the world's poorest countries.

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So, how will cities need to change

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to accommodate this growth?

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First, the world will need to seek ways

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to provide adequate food,

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sanitation,

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and education for all people.

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Second, growth will need to happen

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in a way that does not damage the land

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that provides us with the goods and services

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that support the human population.

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Food production might move

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to vertical farms and skyscrapers,

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rooftop gardens,

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or vacant lots in city centers,

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while power will increasingly come

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from multiple sources of renewable energy.

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Instead of single-family homes,

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more residences will be built vertically.

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We may see buildings that contain everything

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that people need for their daily life,

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as well as a smaller, self-sufficient cities

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focused on local and sustainable production.

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The future of cities is diverse,

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malleable,

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and creative,

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no longer built around a single industry,

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but reflecting an increasingly connected

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and global world.